Accumulation type fuel injection system

ABSTRACT

A common rail of an accumulation type fuel injection system has a common rail main body, distributing portions and accessory portions. The common rail main body provides an accumulation chamber for accumulating high-pressure fuel discharged from a high-pressure supply pump. The distributing portion can be connected with a pressure introduction pipe for introducing the accumulated high-pressure fuel to an injector mounted to a cylinder. The accessory portion is disposed on a fuel outlet side of the distributing portion and is connected with the distributing portion and the high-pressure pipe in thread connection. The accessory portion has a sealing member between the accessory portion and a connection object on the distributing portion side. The sealing member has a sealing surface formed substantially in the shape of a spherical surface on the connection object side.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by referenceJapanese Patent Application No. 2002-332703 filed on Nov. 15, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an accumulation type fuel injectionsystem, in particular to sealing structure of an accumulation device ofthe accumulation type fuel injection system.

2. Description of Related Art

As one of accumulation type fuel injection systems, a common rail typefuel injection system for a diesel engine having a high-pressure supplypump and a common rail is known, for instance. The high-pressure supplypump is rotated by a crankshaft of the diesel engine so that the supplypump pressurizes fuel drawn from a fuel tank and discharges thehigh-pressure fuel. The common rail functions as a kind of surge tankfor accumulating the high-pressure fuel discharged from thehigh-pressure supply pump.

The fuel is accumulated in the common rail at a relatively high pressure(a pressure 100 to 1000 times as high as the atmospheric pressure, ormore). The accumulated fuel is supplied to combustion chambers ofcylinders by injection through injectors mounted on the cylinders. Acertain common rail as the accumulation device of this kind hasstructure in which a flow limiter is attached to the common rail asshown in FIG. 4. The flow limiter stops the fuel supply to the injectorif the high-pressure fuel is injected from the injector excessively. Inthe common rail structure, the common rail is formed in a deformed shapeso that a thickened screw portion, which is screwed and connected withthe flow limiter, and a common rail main body are formed in a singlepiece. Since the common rail is formed into the deformed shape in asingle piece, processing accuracy in perpendicularity between a centralaxis of the screw portion and a flat surface of a flat sealing portionof the common rail main body can be achieved easily and high-pressuresealing structure can be maintained.

As shown in FIG. 4, the flow limiter has a body formed with a screwportion screwed with the common rail, a valve member capable of movingin an axial direction in the body, and a spring for biasing the valvemember toward the flat sealing portion. The flat sealing portioncontacts a lower end surface of the valve member to define an initialposition of the valve member so that a moving distance of the valvemember in the axial direction is set to a predetermined distance. Thevalve member moves in the axial direction in accordance with an upstreamand downstream pressure difference.

However, the common rail having the structure of the conventionaltechnology is the deformed product formed by forging and the like.Therefore, there is a problem that production cost is relatively high.

A joined common rail can be employed as a countermeasure to the aboveproblem. The joined common rail is made by forming the common rail mainbody and the thickened screw portion as separate parts and by joiningthe thickened screw portion to the common rail main body into the singlecommon rail by welding and the like. The thickened screw portion and thecommon rail main body formed as the separate parts are joined with eachother with heat by welding, in which both the thickened screw portionand the common rail main body are melted, or by blazing with blazingfiller. Therefore, under some welding conditions or blazing conditions,there is a possibility that a central axis of a threaded portion of thethickened screw portion may not become perpendicular to the flat surfaceof the flat sealing portion, and the thickened screw portion may bejoined in an inclined state. In this case, there is a possibility thatthe flat sealing portion may contact a sealing portion of the flowlimiter unevenly. As a result, high-pressure sealing performance may bedegraded.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anaccumulation type fuel injection system, which is formed in inexpensivestructure and is capable of improving high-pressure sealing performance.

It is another object of the present invention to provide an accumulationtype fuel injection system having an accumulation device, which has anaccessory portion corresponding to a safety device and suppliesaccumulated high-pressure fuel though the accessory portion, so that theaccumulation type fuel injection system is formed in inexpensivestructure and is capable of improving high-pressure sealing performance.

According to an aspect of the present invention, an accumulation typefuel injection system has a high-pressure supply pump, which is drivenby an internal combustion engine to rotate so that the high-pressuresupply pump pressurizes and discharges drawn fuel, and an accumulationdevice for accumulating the high-pressure fuel discharged from thehigh-pressure supply pump. The accumulation type fuel injection systemsupplies the accumulated high-pressure fuel to cylinders of the internalcombustion engine through injectors mounted to the cylinders. Theaccumulation device has a common rail main body, distributing portionsand accessory portions. The common rail main body is formed with anaccumulation chamber for accumulating the high-pressure fuel. Thedistributing portion can be connected with a pressure introduction pipefor introducing the high-pressure fuel accumulated in the common railmain body to each injector. The accessory portion is disposed on a fueloutlet side of the distributing portion and is connected to thedistributing portion and the pressure introduction pipe in threadconnection. Each accessory portion has a sealing member between theaccessory portion and a connection object on the distributing portionside, to which the accessory portion is connected in thread connection.A sealing surface of the sealing member on the connection object side isformed in the shape of a substantially spherical surface.

Thus, the accumulation device (the common rail) as a kind of surge tankof the above accumulation type fuel injection system for accumulatinghigh-pressure fuel supplied to the respective cylinders of the internalcombustion engine has the common rail main body, the distributingportions and the accessory portions. The distributing portion can beconnected with the pressure introduction pipe corresponding to eachcylinder. The accessory portion is disposed on an outlet side of thedistributing portion and is connected with the distributing portion andthe pressure introduction pipe in thread connection. In this case,generally, each accessory portion has to be screwed to a threadedportion formed on an inner peripheral surface of the distributingportion, and an end surface of the accessory portion and an innermostsurface on an inner peripheral side of the distributing portion have tobe sealed. For instance, sealing performance can be maintained suitablyby improving processing accuracy in perpendicularity of a sealingsurface with respect to a central axis of the threaded portion. However,production cost of process such as a threading process of the threadedportion through a forging process or a cutting process is increased.Specifically, compared to the processing of an external surface, theprocessing accuracy in the perpendicularity between a female thread andthe innermost surface is difficult to achieve in the case where thefemale thread, or an internal surface, is processed.

On the contrary, the sealing member having a sealing surface in theshape of a substantially spherical surface on the connection object sideis disposed between the accessory portion and the connection object onthe distributing portion side. The accessory portion is connected to thedistributing portion in thread connection. Therefore, even if theinclination of a central axis of the threaded portion remains deviated,or even if the accessory portion remains inclined, the sealing membercan be connected to the connection object through the spherical surfaceof the sealing member, while the sealing member is positionedarbitrarily.

Accordingly, even in the case where the inclination of the central axisof the threaded portion is deviated, a fastening force generated by thethread connection can be applied to the connection object stably throughthe sealing member having the spherical surface. Therefore, variation inprocessing accuracy is permitted, so inexpensive structure is achieved.Sealing performance can be improved by employing the connectionstructure for connecting the accessory portion to the connection objectin thread connection through the sealing member having the sphericalsurface.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of an embodiment will be appreciated, as well asmethods of operation and the function of the related parts, from a studyof the following detailed description, the appended claims, and thedrawings, all of which form a part of this application. In the drawings:

FIG. 1 is a schematic structural diagram showing a common rail type fuelinjection system according to the present embodiment of the presentinvention;

FIG. 2 is a cross-sectional diagram showing a common rail shown in FIG.1 taken along the line II—II;

FIG. 3 is an enlarged fragmentary diagram showing an area III in FIG. 2;and

FIG. 4 is a cross-sectional view showing a common rail of a conventionalcommon rail type fuel injection system.

DETAILED DESCRIPTION OF THE REFERRED EMBODIMENT

Referring to FIG. 1, a common rail type fuel injection system as anaccumulation type fuel injection system of the present embodiment of thepresent invention is illustrated. The common rail type fuel injectionsystem in FIG. 1 is mounted to a diesel engine.

As shown in FIG. 1, the common rail type fuel injection system has aplurality of (four, in the present embodiment) injectors 2, ahigh-pressure supply pump 3, a common rail 4, and an electronic controlunit (an ECU) 10. The injectors 2 are mounted to respective cylinders ofa multi-cylinder internal combustion engine (a multi-cylinder engine) 1such as a multi-cylinder diesel engine. The high-pressure supply pump 3is driven by the multi-cylinder engine 1 to rotate. The common rail 4functions as the accumulation device for accumulating the high-pressurefuel discharged from the high-pressure supply pump 3. The ECU 10electronically controls the plurality of injectors 2. The ECU 10 is acontrol device for controlling the engine 1. The ECU 10 is controllingmeans for controlling the high-pressure supply pump 3 and the like, inaddition to the injectors 2.

The injector 2 is a fuel injection valve mounted to a combustion chamberof each cylinder of the multi-cylinder engine 1 for supplying thehigh-pressure fuel into the combustion chamber by injection. The ECU 10electronically controls start and stop of energization to an injectionperiod controlling electromagnetic valve (injection period varyingmeans) 2 a as an actuator. Thus, the ECU 10 determines characteristicsof the fuel injection into the combustion chamber of the multi-cylinderengine 1 from the injector 2 such as fuel injection quantity or fuelinjection timing. The injector 2 mounted to each cylinder of themulti-cylinder engine 1 supplies the high-pressure fuel accumulated inthe common rail 4 into the combustion chamber of the cylinder while theinjection period controlling electromagnetic valve 2 a is open.

The high-pressure supply pump 3 has a known low-pressure feed pump, aplunger and a pressurizing chamber (a plunger chamber). A pump drivingshaft 12 rotates in accordance with the rotation of a crankshaft 11 ofthe multi-cylinder engine 1, so the low-pressure feed pump draws thefuel from a fuel tank 9. The plunger is driven by the pump driving shaft12. The pressurizing chamber pressurizes the fuel by reciprocatingmotion of the plunger. The high-pressure supply pump 3 is a supply pumpfor pressurizing the fuel drawn by the low-pressure feed pump through afuel pipe 13 and for discharging the fuel to the common rail 4. An inletflow control valve (an injection pressure controlling electromagneticvalve) 7 is disposed on an inlet side of a fuel passage leading to thepressurizing chamber of the high-pressure pump 3. The inlet flow controlvalve 7 functions as an actuator for opening or closing the fuelpassage. The inlet flow control valve 7 is a flow control valve as adischarge quantity controlling electromagnetic valve for controlling thedischarging quantity of the fuel discharged from the high-pressuresupply pump 3 to the common rail 4. The inlet flow control valve 7 iselectronically controlled by a control signal from the ECU 10. The inletflow control valve 7 is controlled by the ECU 10 to regulatepressure-feeding quantity, or discharging quantity, of the high-pressurefuel pressure-fed from the high-pressure supply pump 3 to the commonrail 4 through a fuel pipe 16. Thus, the inlet flow control valve 7functions as injection pressure varying means for varying the injectionpressure for injecting the fuel from the respective injectors 2 into thecombustion chambers of the multi-cylinder engine 1.

The common rail 4 is a kind of surge tank for accumulating the fuel at arelatively high pressure (a common rail pressure 100 to 1000 times ashigh as the atmospheric pressure, or more) and is the accumulationdevice for accumulating the high-pressure fuel at the common railpressure. The common rail 4 is required to continuously andfluid-tightly accumulate the high common rail pressure corresponding tofuel injection pressure. Therefore, the common rail 4, the fuel passagefor introducing the high-pressure fuel from the high-pressure supplypump 3 to the common rail 4 and the fuel passages for introducing thehigh-pressure fuel from the common rail 4 to the injectors 2 arerequired to have mechanical strength and high pressure tightness enoughto withstand the common rail pressure. Therefore, the fuel pipe 16 forintroducing the high-pressure fuel from the high-pressure supply pump 3to the common rail 4 is provided as a high-pressure fuel passage formedof a pressure introduction pipe (a high-pressure pipe) such as aninjection steel pipe capable of fluid-tightly connecting thehigh-pressure supply pump 3 with the common rail 4. The fuel passagesfor introducing the high-pressure fuel from the common rail 4 to theinjectors 2 are provided by high-pressure pipes 15 formed ofhigh-pressure fuel passages capable of fluid-tightly connecting thecommon rail 4 with the injectors 2.

A pressure limiter 6 is mounted to the common rail 4 for preventing thecommon rail pressure in the common rail 4 from exceeding a limitaccumulation pressure. The pressure can be released through the pressurelimiter 6. Return fuel from the pressure limiter 6, leak fuel from theinjectors 2 and overflow fuel from the high-pressure supply pump 3 isreturned to the fuel tank 9 through leak pipes (low-pressure pipes) 14as low-pressure fuel passages.

The ECU 10 is a known microcomputer including a CPU for performingcontrol processing and calculation processing, ROM for storing variousprograms and data, RAM for storing input data, an input circuit, anoutput circuit, a power source circuit, an injector driving circuit anda high-pressure pump driving circuit. Sensor signals outputted fromvarious sensors are inputted to the microcomputer after the sensorsignals are converted from analog signals to digital signals by an A/Dconverter. The ECU 10 includes injection quantity and fuel injectiontiming determining means, injection pulse width determining means andinjector driving means. The injection quantity and fuel injection timingdetermining means determines optimum injection timing (injection starttiming) and the fuel injection quantity (an injection periodcorresponding to the fuel injection quantity) in accordance with anoperating condition of the multi-cylinder engine 1. The injection pulsewidth determining means calculates an injector injection pulse having aninjection pulse period (injection pulse width) corresponding to theoperating condition of the multi-cylinder engine 1 and the fuelinjection quantity. The injector driving means applies the injectionperiod controlling electromagnetic valve 2 a of the injector 2 of eachcylinder with the injector injection pulse through the injector drivingcircuit (EDU). The ECU 10 also functions as discharge quantitycontrolling means for calculating the optimum fuel injection pressure,or the optimum common rail pressure, in accordance with the operatingcondition of the multi-cylinder engine and for performing drivingcontrol of the injection pressure controlling electromagnetic valve 7 ofthe high-pressure supply pump 3 through the high-pressure pump drivingcircuit (EDU). The ECU 10 calculates the fuel injection quantity, theinjection timing and the target common rail pressure by using operatingcondition detecting means for detecting the signals representing theoperating condition of the multi-cylinder engine 1 such as a rotationspeed sensor 41 for sensing rotation speed of the multi-cylinder engine1, an accelerator position sensor 42 for sensing a depressed degree ofan accelerator pedal (an accelerator position), and a cooling watertemperature sensor 43 for sensing cooling water temperature. The fuelinjection quantity, the injection timing and the target common railpressure may be corrected by considering detection signals (engineoperation information) from other sensors 44 as the operating conditiondetecting means such as an intake temperature sensor, a fuel temperaturesensor, an intake pressure sensor, a cylinder determination sensor andan injection timing sensor.

Next, the common rail 4 as the accumulation device as a substantial partof the accumulation type fuel injection system of the present inventionwill be explained based on FIGS. 1, 2 and 3. As shown in FIG. 1, thecommon rail 4 has a common rail main body 4 a, inside which anaccumulation chamber 4 c for accumulating the high-pressure fuel isformed, and distributing portions 4 b, which can be connected with thehigh-pressure pipes 15 for introducing the high-pressure fuelaccumulated in the common rail main body 4 a to the injectors 2 of therespective cylinders.

The common rail main body 4 a is formed into a predetermined shapethrough a forging process, a cutting process for cutting its entiresurface, a drawing process or a flatting process. As the predeterminedshape of the common rail main body 4 a, the common rail main body 4 a isformed substantially in the shape of a relatively thick pipe. Across-section of the accumulation chamber 4 c formed inside the commonrail main body 4 a is formed substantially in the shape of a round or anellipse. The accumulation chamber 4 c extends in a longitudinaldirection of the common rail main body 4 a (in a lateral direction inFIG. 1). Thus, the common rail 4 has a simple shape, which can be easilyformed through the drawing process or the flatting process. Therefore,production cost for processing is reduced.

In the case where the common rail main body 4 a is formed by forging,the common rail main body 4 a is merely formed substantially into theshape of a pipe. Therefore, compared to the forged product formed intothe deformed member having the conventional structure shown in FIG. 4,structure of a forging die can be simplified and the increase in theprocessing cost of the forging process can be inhibited.

The distributing portion 4 b is formed substantially in the shape of acylinder as shown in FIG. 2. The distributing portions 4 b and thecommon rail main body 4 a are formed as separate parts in advancethrough separate processes, for instance. Then, the common rail mainbody 4 a and the distributing portions 4 b are integrated by welding orbrazing. The distributing portions 4 b connected with the common railmain body 4 a branch substantially perpendicularly to the longitudinaldirection of the common rail main body 4 a, in which the accumulationchamber 4 c extends, as shown in FIGS. 1 and 2. Thus, the high-pressurefuel is distributed toward the injectors 2 disposed in the respectivecylinders of the multi-cylinder engine 1.

Thus, the common rail main body 4 a and the distributing portions 4 bare formed as the separate parts and are integrated by the welding andthe like. Therefore, unlike the conventional forged product, there is noneed to form the common rail 4 in a single piece by shaping acomplicated and deformed member. Thus, the production cost can bereduced. The common rail main body 4 a, to which the distributingportions 4 b are connected, should preferably have cylindrical portions4 a 1 formed substantially concentrically with connection objects(innermost surfaces, sealing surfaces) 4 s on the sides of thedistributing portions 4 b respectively, and stepped surfaces 4 a 2formed around the cylindrical portions 4 a 1 respectively. Thus, aninner periphery of each distributing portion 4 b can be connected to thecylindrical portion 4 a 1. Meanwhile, a connecting area for connecting alower end surface of the distributing portion 4 b with the steppedsurface 4 a 2 by welding can be ensured easily.

Moreover, in the present embodiment, as shown in FIGS. 1 and 2, anaccessory portion (a flow limiter) 4 h corresponding to a safety deviceis disposed on an outlet side of each distributing portion 4 b. Theaccessory portion 4 h is connected with the distributing portion 4 b andthe high-pressure pipe 15 in thread connection respectively. Moreover,as shown in FIG. 1, the accessory portion 4 h and the distributingportion 4 b seal a lower end surface 4 h 2 of the accessory portion 4 hand the innermost surface 4 s formed radially inside the inner peripheryof the distributing portion 4 b, at which a threaded portion 4 b 1 forthe thread connection is formed, through a sealing member 4 d with afastening axial force generated by the thread connection.

The accessory portion 4 h is screwed with the threaded portion 4 b 1formed on an inner peripheral surface of the distributing portion 4 b.An end portion (a lower end surface) 4 h 2 of the accessory portion 4 hand the innermost surface 4 s radially inside the distributing portion 4b are required to be sealed so that high-pressure sealing performance ismaintained. In this case, generally, accuracy of form related tophysical relationship between the threaded portion 4 b 1 of thedistributing portion 4 b, which partially or entirely accommodates theaccessory portion 4 h, and the innermost surface 4 s has to be improved.For instance, processing accuracy of the perpendicularity between theflat surface of the flat sealing surface as the connection object andthe central axis of the threaded portion has to be improved like theconventional structure shown in FIG. 4. By improving the processingaccuracy, the high-pressure sealing performance can be improved.However, the processing cost will be increased. For instance, in thecase of the forged common rail, a die accuracy of a die used in theforging pressing has to be improved. As a result, the processing cost isincreased.

On the contrary, in the present embodiment, as shown in FIGS. 2 and 3,the sealing member 4 d having a fuel passage 4 d 3 is disposed betweenthe accessory portion 4 h and the sealing surface 4 s as the connectionobject on the distributing portion 4 b side, to which the accessoryportion 4 h is connected in the thread connection. A sealing surface 4 d1 of the sealing member 4 d on the connection object 4 s side is formedsubstantially in the shape of a spherical surface. The sealing surface 4s as the connection object is formed in the shape of a conical surfaceas shown in FIGS. 2 and 3. Therefore, the sealing member 4 d can beconnected to the connection object 4 s even if the axis, or a position,of the sealing member 4 d is set arbitrarily with respect to theconnection object 4 s. As a result, the accessory portion 4 h, thesealing member 4 d and the connection object 4 s on the distributingportion 4 b side can contact each other fluid-tightly in a state inwhich the inclinations of the central axes of the accessory portion 4 hand the sealing member 4 d are deviated from the central axis of theconnection object 4 s. More specifically, even in the case where thepositional accuracy in the physical relationship between the threadedportion 4 b 1 and the connection object 4 s is set within apredetermined tolerance, the fastening axial force generated by screwingthe accessory portion 4 h can be applied evenly to the spherical surface4 d 1 of the sealing member 4 d, the substantially conical surface ofthe connection object 4 s and a sealing portion of the accessory portion4 h in a state in which the central axis of the threaded portion 4 b 1is inclined within the tolerance, or in the state in which the accessoryportion 4 h fitted to the threaded portion 4 b 1 in the threadconnection remains inclined.

Therefore, the high-pressure sealing performance can be improved withoutincreasing the processing accuracy of the threaded portion 4 b 1 and theconnection object 4 s even in the case where the positional accuracy isset within the predetermined tolerance. As a result, the production costcan be reduced, and meanwhile, the common rail 4 as the accumulationdevice capable of improving the high-pressure sealing performance can beproduced.

In the above embodiment, the threaded portion 4 b 1 formed on thedistributing portion 4 b, which is integrated with the common rail mainbody 4 a by welding and the like, is the thread formed on the innerperipheral surface of the distributing portion 4 b, or the femalethread. Alternatively, the threaded portion 4 b 1 may be a male threadformed on an outer peripheral surface of the distributing portion 4 b.The processing for achieving a predetermined positional accuracy in thecentral axis of the threaded portion 4 b 1 with respect to theconnection object 4 s is more difficult in the case where the femalethread is formed than in the case where the male thread is formed byprocessing the outer peripheral surface. In the case where the sealingmember 4 d having the spherical surface 4 d 1 is employed, the effect ofreducing the production cost is relatively great in the case where thethreaded portion 4 b 1 is formed on the inner peripheral surface of thedistributing portion 4 b.

The present invention can be suitably applied to the structure in whichthe common rail main body 4 a and the distributing portions 4 b areformed as the separate parts in the preceding process, and the commonrail main body 4 a and the distributing portions 4 b are integrated bythe welding or the brazing. Thus, the fastening force generated byscrewing the accessory portion 4 h and the distributing portion 4 b witheach other can be applied stably to the connection object 4 s throughthe sealing member 4 d having the spherical surface 4 d 1, even in thecase where the central axis of the threaded portion 4 b 1 of thedistributing portion 4 b is inclined with respect to the connectionobject 4 s. The inclination of the central axis of the threaded portion4 b 1 is caused under some melting conditions at the welded surfaces ofthe common rail main body 4 a and the distributing portion 4 b or undersome brazing conditions of the brazing with the brazing filler. Thus,the inexpensive structure can be compatible with the improvement of thehigh-pressure sealing performance.

The accessory portion (the flow limiter) 4 h has a body 4 hb, a valvemember 4 hv and a spring 4 hs. The body 4 hb is formed with a screw 4 h1, which is threaded to the distributing portion 4 b. The valve member 4hv is capable of reciprocating in an axial direction in the body 4 hb.The spring 4 hs biases the valve member 4 hv toward a root of thedistributing portion 4 b (toward the common rail main body 4 a). Theaccessory portion 4 h is a safety device for stopping the fuel supplyfrom the common rail 4 to the injector 2 in the case where the injector2 injects the high-pressure fuel excessively. Thus, in a normal state,the accessory portion 4 h functions as a part of the fuel passageconstituting the distributing portion 4 b for introducing thehigh-pressure fuel to the injector 2. On the other hand, only in thecase where the injector 2 injects the high-pressure fuel excessively,the accessory portion 4 h functions as the safety device to limit thesupply of the high-pressure fuel to the injector 2.

In the present embodiment, as shown in FIG. 2, a restrictor 4 hv 1 isformed in the valve member 4 hv for connecting an upstream side and adownstream side of the valve member 4 hv. When the high-pressure fuelflows toward the injector 2 from the accumulation chamber 4 c of thecommon rail main body 4 a through the accessory portion 4 h, a pressuredifference (an upstream and downstream pressure difference) is generatedbetween the upstream side and the downstream side of the valve member 4hv by a restricting effect of the restrictor 4 hv 1. The upstream anddownstream pressure difference increases as the flow rate of thehigh-pressure fuel increases. As shown in FIG. 2, the accessory portion4 h has known valve structure in which a maximum travel distance of thevalve member 4 hv is defined by a separation distance L between astepped fuel passage formed on an inner surface of the body 4 hb and thevalve member 4 hv, and the maximum travel distance L is set to adistance corresponding to a maximum limit fuel supply flow rate.

In the present embodiment, the valve member 4 hv contacts the sealingmember 4 d, so an initial position of the valve member 4 hv fordetermining the maximum travel distance L of the valve member 4 hv islimited as shown in FIG. 2. A surface of the sealing member 4 dsubstantially opposite from an end surface 4 d 2 of the sealing member 4d, at which the sealing member 4 d contacts the valve member 4 hv, isformed into the substantially spherical surface 4 d 1, which contactsthe conical sealing surface 4 s as the connection object. The endsurface 4 d 2 is formed in the shape of a flat surface as shown in FIG.2. Thus, even in the case where the central axis of the threaded portion4 b 1 of the distributing portion 4 b is inclined, the body 4 hb and thesealing member 4 d contact each other at entire peripheries thereof asshown in FIGS. 2 and 3, without partially contacting each other. It isbecause the sealing surface 4 d 1 of the sealing member 4 d is formedsubstantially in the shape of the spherical surface, and the sealingmember 4 d contacts the substantially conical sealing surface 4 s in astate where the substantially spherical sealing surface 4 d 1 isinclined along the conical sealing surface 4 s. Therefore, the valvemember 4 hv can contact the end surface 4 d 2 of the sealing member 4 dstably, and the initial position of the valve member 4 hv fordetermining the maximum travel distance L of the valve member 4 hv canremain stabled even in the case where the central axis of the threadedportion 4 b 1 is inclined.

In the present embodiment, the accessory portion 4 h is explained as theflow limiter. However, the accessory portion 4 h is not limited to theflow rate limiting device such as the flow limiter for limiting thesupply quantity of the high-pressure fuel. Alternatively, any safetydevice such as a pressure limiting device including the pressure limiter6, which limits the common rail pressure under the permissible pressureby returning the fuel, which provides the excessively high pressure, tothe low-pressure fuel passage 14 in the case where the pressure of thehigh-pressure fuel becomes excessively high, may be employed as theaccessory portion 4 h. Alternatively, any other device can be employedas the accessory portion 4 h if the device does not degrade the functionof supplying the high-pressure fuel from the common rail 4 to theinjector 2 in the normal state.

The present invention should not be limited to the disclosed embodiment,but may be implemented in many other ways without departing from thespirit of the invention.

1. An accumulation type fuel injection system having a high-pressuresupply pump, which is driven by an internal combustion engine to rotateso that the high-pressure supply pump pressurizes and discharges drawnfuel, and an accumulation device for accumulating the high-pressure fueldischarged from the high-pressure supply pump, the accumulation typefuel injection system supplying the accumulated high-pressure fuel tocylinders of the internal combustion engine through injectors mounted tothe cylinders, wherein; the accumulation device has a common rail mainbody providing an accumulation chamber for accumulating thehigh-pressure fuel, distributing portions capable of being connectedwith pressure introduction pipes for introducing the high-pressure fuelaccumulated in the common rail main body to the injectors respectivelyand accessory portions, which are disposed on fuel outlet sides of thedistributing portions and are connected with the distributing portionsand the pressure introduction pipes respectively in thread connection,and the accessory portion has a sealing member between the accessoryportion and a connection object on the distributing portion side, towhich the accessory portion is connected in thread connection, thesealing member having a sealing surface substantially in the shape of aspherical surface on the connection object side.
 2. The accumulationtype fuel injection system as in claim 1, wherein the distributingportions and the common rail main body are formed as separate parts andare integrated through a joining process.
 3. The accumulation type fuelinjection system as in claim 2, wherein the distributing portions andthe common rail main body are integrated through a welding process or abrazing process.
 4. The accumulation type fuel injection system as inclaim 2, wherein; the common rail main body is formed of an injectionsteel pipe made through a drawing process or a flatting process, and thedistributing portion is formed of a forged product or a cut productsubstantially in the shape of a cylinder, wherein the distributingportion has a threaded portion on an inner peripheral surface thereofnear an end thereof.
 5. The accumulation type fuel injection system asin claim 1, wherein the accessory portion is a safety device forstopping the fuel supply from the accumulation device to the injector inthe case where the injector injects the high-pressure fuel excessively.6. The accumulation type fuel injection system as in claim 5, wherein;the accessory portion has a body, which is formed with a screw threadedto the distributing portion, a valve member, which is capable of movingin an axial direction inside the body, and a biasing spring for biasingthe valve member toward the distributing portion, and the valve membercontacts a surface of the sealing member substantially opposite from thesealing surface on the connecting object side so that an initialposition of a travel distance of axial movement of the valve member isdefined.
 7. The accumulation type fuel injection system as in claim 1,wherein the connection object is formed substantially in the shape of aconical surface.